The need for intumescent seals on fire doors

[bungle]

Auntie Lin, Please check your messages.

Bungle

[nearlythere]

Door stop size does not make a significant difference to the fire resistance rating of a timber doorset

I would agree if the doorset was fitted with intumescent strip and the 12mm stop would most probably more effective. But to make these comparisons you would have to see the doorsets tested without intumescent strips was this the case?

If so you must be an old git like me.

Door stop size does not make any difference to the smoke sealing ability of a timber doorset (TRADA did some research that demonstrated this, I seem to recall)

I would be very interested in this research do you have any further details? I would like to know the amount of leakage to determine the threat to a means of escape?

Yes - not an old git, but a git nonetheless.  Seen them tested without the intumescent strips & they do around 15 mins, depending upon construction & fitting.  You can intuitively conceive that the size of the door stop will make no significant difference if the fire is on the opening side of the door, and this is borne out by 'real' tests.

Playing devil's advocate here, would you not agree intumescent strips are really for property protection, rather than life safety (other than in premises where there is a stay put policy)

Disagree, I'm afraid.  The only reason that we have them is that they are required so that timber doorsets meet the fire resistance performance referred to in the National guidance to the Building Regulations (e.g. the ADB in England & Wales).  These Regulations have nothing to do with property protection - only life safety.

Fishy.
Check your messages.

[Clevelandfire 3]

Playing devil's advocate here, would you not agree intumescent strips are really for property protection, rather than life safety (other than in premises where there is a stay put policy)

Disagree, I'm afraid.  The only reason that we have them is that they are required so that timber doorsets meet the fire resistance performance referred to in the National guidance to the Building Regulations (e.g. the ADB in England & Wales).  These Regulations have nothing to do with property protection - only life safety.

Oh so that automatically and magically makes them a life safety consideration.Im not sure if your post was made tongue in cheek or not. WHat you summise may apply to new build but what about existing properties? Tell you what why not try enforcing that in a hotel with 60 bedroom doors that need upgrading and see how far you get.

[Fishy]

Oh so that automatically and magically makes them a life safety consideration.Im not sure if your post was made tongue in cheek or not. WHat you summise may apply to new build but what about existing properties? Tell you what why not try enforcing that in a hotel with 60 bedroom doors that need upgrading and see how far you get.

Well... yes it does.  Nothing in the Building Reg's is there to provide property protection per se (admittedly some of the recommendations do relate to fire spread outside the premises of origin).  For England & Wales this is spelt out right at the front of the ADB (I quote): "...Building Regulations do not require anything to be done except for the purpose of securing reasonable standards of health and safety for persons in or about buildings (and any others who may be affected by buildings or matters connected with buildings)...".  Since the Approved Documents are solely to provide 'good practice' guidance on compliance with those Regulations, it follows that the performance requirements detailed therein relate to life safety only.  This isn't my opinion - it's there in black & white.

What I'm saying is that it's an upgrade option that is too easily dismissed - and that the determination that I referred to (http://www.communities.gov.uk/documents/fire/pdf/heritagehotel.pdf) gives you a flavour of how our Regulators view this issue (and bear in mind that this applies to a Grade 1 listed building, where the arguments for leaving the existing doors 'as is' would be stronger than the run-of-the-mill hotel).

[CivvyFSO]

If that is the determination I am thinking of then they are talking about doors where the hotel owner/employer had admitted that the doors in question would barely last 10 minutes in a fire. That is quite different to asking for an upgrade on an old fire door that just doesn't have the strips & seals.

[Fishy]

If that is the determination I am thinking of then they are talking about doors where the hotel owner/employer had admitted that the doors in question would barely last 10 minutes in a fire. That is quite different to asking for an upgrade on an old fire door that just doesn't have the strips & seals.

...not sure why - when the "old fire door that just doesn't have the strips & seals" could well do only 15mins in a test, no matter how thick & heavy it is?

In any case I’m not saying upgrade everything; I’m saying that if you don’t have fire-resisting doorsets that comply with current good practice as regards fire and smoke resistance then you need to understand that and assess the consequences.  In fire safety (as in other areas of health & safety) acceptability tends to be judged against such good practice, so if you don’t comply you should always be ready to justify why not. If you can’t do that then you have to upgrade your fire precautions – affordability is no excuse not to, under the Law.
 
As I said in an earlier post, in my opinion compromising on smoke resistance is much harder than compromising on fire resistance.  The only way you will get cold smoke resistance to any defined level is to fit seals – stop size, closeness of fit or whatever won’t make any significant difference.  If you’re fitting smoke seals you may as well fit combined intumescent/smoke seals.  It isn’t necessarily difficult & it isn’t necessarily expensive (you can even get thin surface-mounted seals that can be self-applied by the owner – Google ‘surface mounted intumescent strip’).

As regards the determination – as I said, it gives a ‘flavour’ of how the Regulators view the issue of upgrading timber fire doors. It clearly states that it only applies to the particular circumstances of the case, however If we’re advising our clients with the aim (amongst other things) of satisfying those regulators, it’s an example that we must be mindful of.

[Midland Retty]

Hi Fishy

I can't argue with anything you have said, and each scenario has to be assesed on its own merits.

Despite that I still fail to see the life safety benefit of intumescent strips in most situations, even most sleeping risks infact.

I can see the benefit in buildings with stay put policies, or large high rise buildings where it would take a substantial amount of time for people to evacuate.

Perhaps one of the reasons I question the issue of intumescent strips stems from the fact that I can count on one hand the amount of times I've visted a fire scene to find that intumescents strips have activated.



 

[Tom Sutton]

I had a further enquiry about FD20 doors and during my research I found an information leaflet from BWF at http://www.bwf.org.uk/fileadmin/documents/assets/FD_2020_20explanation.pdf . Which in my interpretation says a fire doors without intumescent seals can only achieve 20 mins providing it has been fitted to a high standard. A fire door with the same specification and intumescent seals can achieve 30mins consequently if a situation requires 30 mins fire protection then intumescent seals need to be fitted. simples?

[Auntie LIn]

Tom - you're quite right.   It's a myth that a door that achieves FD30 with seals will do 20 without.   We did some testing while I was at TRADA (ok - it was last century!) which showed that it was more likely that 17 or 18 minutes would be the common level achieved.   In these days of assessing risk, you may consider 17 minutes to be quite adequate, depending on other measures which would offset this reduction but as you point out, the achievement of 20 minutes has to be down to the excellence of fit of the leaf in the frame, and a very stable leaf construction which isn't going to bow like b..... blazes.

[Clevelandfire 3]

Auntie Lynn do we know why fire doors fitted with intumescents lasted longer than those fitted without?. Midland Retty got me thinking about how many times ive seen intumescent strips activate. Not many. So im quite confused.Are the tests conducted slightly flawed and unrealistic because unless you have a fire right against the door i cant see how unactivated strips will give better protection.

[Tom Sutton]

I suspect the reason why you do not see many cases where the intumescent seals have activated is because it is only likely to happen at the seat of the fire or the room of origin where the temperature are high enough and this area is usually damaged beyond recognition after the fire. The rest of the building may be seriously smoke and heat damaged but the temperatures are unlikely to rise high enough to activate the seals.

You must have done a stint in the control tower at Moreton during an exercise on the fire-ground and witnessed the temperatures the can be achieved in the fire houses (1000 degrees F or C  ).  

[Auntie LIn]

Auntie Lynn do we know why fire doors fitted with intumescents lasted longer than those fitted without?. Midland Retty got me thinking about how many times ive seen intumescent strips activate. Not many. So im quite confused.Are the tests conducted slightly flawed and unrealistic because unless you have a fire right against the door i cant see how unactivated strips will give better protection.

Cleveland - the reason why doors with fire seals last longer than those without is simply that fire and smoke seek out the path of least resistance.   In the case of a door, it's primarily the gap between the leaf and the frame.   When you burn wood, it dries out and shrinks a little bit, and also can deflect.   This increases the ease with which fire can pass from one side of the door to the other.....and so on.   Don't believe the old myth about the value of a 25mm deep doorstop.   If you're looking for something crucial to improve the performance of a doorset, start with gaps which are even around the periphery of the leaf and within the manufacturer's tolerances - and this is usually about 3mm.   It's really sad when inspecting officers go round a building and insist on 25mm deep stops when in fact they should have been getting 6-8mm gaps reduced.

The reason you don't see many seals activated in 'real' fire is because so often you chaps get there before the seals can activate.   If the door is on the room of origin (and how many of us can say in advance of a fire which one that will be for sure?) you may see activated seals.   The seals activate at about 140 deg.C   Remember that this is the temperature at the seal -and the seal is set into the leaf/frame junction, so the actual room fire temperature is likely to be 600+ degrees.

If you're interested in knowing about fire testing and seeing how it's done, I think you might find something on the BWF website.   If not there was a video produced by West Birmingham Health Authority (last century I know, but the basic principle is the same) which shows a test being carried out.   Labs such as Chiltern International Fire and Exova Warringtonfire may well have video clips on their websites.   You might also ask a friendly manufacturer if they'll take you along when they next do a test - but you do have to remember that when they are testing it's for the benefit of their business so they might not be very happy about sharing the experience.
 

[Davo]

Cleveland

Adding to Auntie Lin, the IFSA have some factsheets on IS.

http://www.ifsa.org.uk/download.html

Traditionally, the silicate seals activate at about 180 degrees, and as she says, you guys and gals get there damn quick!
The newer carbon seals activate at about 120 and therefore kick off earlier.
If you are serious about upgrading then look at switching types, but do not mix in the same door as this causes deflection as AL has said



davo

[Fishy]

Auntie Lynn do we know why fire doors fitted with intumescents lasted longer than those fitted without?. Midland Retty got me thinking about how many times ive seen intumescent strips activate. Not many. So im quite confused.Are the tests conducted slightly flawed and unrealistic because unless you have a fire right against the door i cant see how unactivated strips will give better protection.

The tests are not really intended to be 'realistic' - they're meant to be representative.  You can't make them realistic unless you duplicate a compartment with the appropriate fire load, ventilation conditions etc, set fire to it & wait for the doorset to fail - this would be impractical, in the vast majority of cases.  What the tests do is enable us to rank fire resistance performance in a repeatable & reproduceable way, so we usually use 30 minute construction to separate means of escape, 60 minutes for high-risk areas etc in the knowledge that the construction probably won't do 30 / 60 minutes in a 'real' fire (it might do more or it might do less), but that we're using kit that has the established and recognised 'good practice' performance required for that risk.  Our regulators have set these requirements/recommendations on the basis that they have been demonstrated to be safe, & that the test is onerous enough to allow a bit of a margin of safety, to cope with some of the vaguaries of installation (& thus performance) you're inevitably going to get in the construction industry.

The subtleties of the testing regime & it's lack of 'reality' are often forgotten - I've lost track of the number of times I've come across people assuming that they can sit behind a one-hour fire resisting construction quite happily for an hour, if there's a fully developed fire on the other side!  I prefer the maritime ratings, where you have 'B', 'A' and 'H' - class fire-resisting structures - being 30, 60 and 120 minutes F/R and separating low-to-high risk areas respectively.  Much less open to misinterpretation!

Having said the above, the tests aren't bad, so long as their limitations are recognised - & it's interesting to note that the standards for fire resistance tests are more or less the same throughout the world (unlike most other types of fire test).

Lastly, on the subject of the seals on fire doors, they have two main functions.  Firstly they expand to stop smoke and hot gases exploiting the gap between the door leaf and the frame (or between the two door leaves, in double doorsets).  Secondly, as Auntie Lin says, timber doors bend and bow when they are attacked by fire from one side - the timber shrinks as it dries out and this causes the door to bow away from the fire at its middle & towards the fire at its corners. This 'dishing' can be very significant and is the main reason that many timber doors fail the test, rather than burning through the bulk of the door leaf.  That's why it's more or less impossible to calculate the fire resistance of timber doors based on charring rates alone, because it doesn't take into account this distortion. Some seals exert enough pressure to 'clamp' the door leaf in the frame and stop the edges bowing out of the rebate.  

There is a third function on non-latched doorsets - they hold the door leaf in the frame once the door closer has stopped working (normally 10 to 15 minutes into the test, if face-fixed).

[Midland Retty]

Hi Auntie Lin & Fishy

I understand completely the rationale behind intumescent strips and the way they are tested. I also understand the behaviour of fire doors during fire. I remain largely unconvinced however that intumescent strips offer any real benefit, other than property protection, in most buildings, and thus care needs to be taken by enforcers and assessors alike as to how far they go when pushing for existing fire doors to be upgraded where they are found not to be of the correct standard.

You could argue that the duty to mitigate the effects of fire under the RRO, and the fact that any fire safety plan should not include any reliance on the fire service means that intumescent strips do still have a role to play in some way shape or form.

But this would only be from a building protection viewpoint, not life safety. (save for some premises such as defend in place strategies or large complex buildings where evacuation would be long and protracted)

More and more buildings nowadays have some form of early warning or detection, early detection means quicker evacuation, and hopefully that means the fire service gets called out much quicker too.

And whilst any fire safety plan shouldn't rely upon fire service intervention, early detection does lead in all but a few case to early intervention.

Ive even been to incidents where the fire has been burning for quite sometime before we were called out, and yet still the intumescent hasn't activated. I dont buy the argument that early intervention is a factor in why we dont see many strips activate.

Imagine you are an enforcer or assessor standing in an 60 bed hotel. The doors to each bedroom are fire resisting to 30 minutes standard, are fitted with cold smoke seals and positive self closing device. There aren't any intumescent strips however.

Are you going to issue them a report saying all bedroom doors should be upgraded within 6 months, or would it not be better to suggest that when the fire doors need to be replaced the new fire doors meet current standards?